1. Field of the Invention
The present invention relates to an oil filter unit and a motorcycle including the oil filter unit.
2. Description of Related Art
A number of metal components such as a cylinder, a piston and a transmission that move at high speed while contacting one another are contained within an engine of a motorcycle. Thus, lubricating oil is supplied to these components using a lubricating device to reduce frictional resistance and obtain sufficient functions from the engine.
Lubricating oil is typically stored in an oil pan disposed below a crank case of an engine, pumped up using an oil pump and filtered by an oil filter. After passing through a main gallery within the crank case, the lubricating oil is supplied with pressure to respective lubrication sections.
Oil passages extending from the oil pump to the main gallery typically cross one another at right angles because of the structure of the crank case. Thus, the attachment face of the oil filter is generally positioned to cross the oil route at right angles (for example, see JP-A-2004-204771).
In some arrangements of the oil pump and attachment positions of the oil filter, however, a number of communication passages are required to form the oil passages. As a result, the number of manufacturing steps necessary for forming the oil passages and communication passages of the crank case increases, and thus the cost rises.
Similar to the oil passages, the communication passages typically cross one another because of the structure of the crank case. It is therefore necessary to dispose the communication passages such that there is no interference between the communication passages and the oil passages. Such an arrangement increases the oil route length and thus lowers the oil pressure in some cases.
A method disclosed in JP-A-2001-227317 simplifies the layout of the oil passages considering these limitations. FIGS. 7(a) and 7(b) show the structure of the engine case (crank case) of JP-A-2001-227317.
As illustrated in FIGS. 7(a) and 7(b), an engine case 101 comprises an upper engine case 101a and a lower engine case 101b. An oil pan 108 is attached to the lower part of lower engine case 101b. Lubricating oil within oil pan 108 is pumped up by an oil pump, and is supplied with pressure from an oil delivery passage 103 through a communication path 104 to an oil filter 105. Then, the lubricating oil filtered by the oil filter passes through an oil supply passage 106 and is guided to a main gallery 107. Thereafter, the lubricating oil flows through other oil supply passages (not shown) to be introduced to the respective lubrication sections within the engine.
In this structure, oil delivery passage 103 and oil supply passage 106 are disposed in parallel with the connection plane between upper engine case 101a and lower engine case 101b, and communication path 104 is disposed in parallel with the connection plane between lower engine case 101b and oil pan 108. In this layout, communication passage 104 is not in parallel with oil delivery passage 103 and oil supply passage 106 and thus does not interfere with oil delivery passage 103 and oil supply passage 106. Thus, the distance between communication passage 104 and oil filter 105 can be decreased to a minimum length.
According to this layout of JP-A-2001-227317, the respective oil passages extending from the oil pump to the main gallery cross one another at right angles. However, the communication path extending from the oil (delivery) passage to the oil filter does not cross the oil passages at right angles. Therefore, this structure is effective in that the communication path does not interfere with the oil passages. However, considering the structure of an engine case, it is extremely difficult to manufacture a communication path which does not cross the oil passages at right angles. Therefore, the manufacturing cost of a layout such as that shown in JP-A-2001-227317 is considerable.